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# Lab9 - setting in the previous activity we place a...

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Conceptual Questions: 1. Because the lens is not always a perfect sphere, so not all lights will focus on the screen. The photographers do so to get rid of the spherical aberration. 2. Human can only see virtual image through the lens. The image cannot be projected onto a surface. This only happens when the object is closer to the lens than its focal length. If the object is further than the focal length, a real image is formed - this is the inverted image. Analysis: Activity1: In this experiment, we are measuring the focal length of a converging lens. First, we find a building that is about 30m away from the window. Next we move screen to find a sharp image. After that, we measure the distance between the screen and the lens. Then we repeat the same procedure on a track. In method 3, we place the converging lens at 2 different positions, and get the distance between the 2 positions. Using the following formula: f=(L 2 -a 2 )/4L, we can find the focal length of the converging lens. Activity2: We are supposed to calculate the focal length of a diverging lens. Using the
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Unformatted text preview: setting in the previous activity, we place a diverging lens about half way between the screen and the converging length. After that, we use the thin-lens equation to get the focal length of the lens. Activity3: In this activity, we use the similar setup as in Activity 1.3, and find a sharp image on the screen. Then we observe the image when we cover half of the lens. And we do the same by covering the peripheral part of the lens, and the center part of the lens. Activity4: We are measuring the index of refraction of a cylindrical lens in this experiment. After getting the refraction angle of different incident angel, we can get the average value of the index of refraction. Then we measure the internal reflection angel and use this formula to find n: n=1/sin(2 θ ). Experimental Error: Measuring error, inaccuracy of human eye, malfunction of the light source, malfunction of the lens....
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